A spindle device of a machine tool which is rotated at high speed and receives high cutting resistance during a cutting operation, may result in a bearing or a collet being damaged or worn, or a disk spring for a tool clamp arranged in a spindle being broken. Such problems in the spindle device may occur not only in the spindle itself but also in the internal structure of the spindle and the bearing. In the case where the spindle device is repaired on the site of operation of the machine tool, it is common practice to remove hydraulic and pneumatic pipes for lubrication, cooling or cleaning, and electrical wiring to the motor and the limit switch, disassemble the whole spindle device, change the spindle, the parts in the spindle or the bearing and then reassemble them. This results in large-scale repair work that requires sophisticated expertise and skill along with considerable time. For this reason, a spindle device generally referred to as a cartridge-type spindle in which the spindle and the bearing can be removed integrally has been developed and disclosed in, for example, U.S. Patent Publication No. 2004/0074074A1.
In recent years, on the other hand, heavy cutting has been required in machine tools in order to reduce machining time. This greatly increases the temperature of the machining area between the cutting edge, of the tool and the workpiece. Therefore, in order to efficiently cool the machining area, a through spindle coolant device has been used in which a coolant or pressured air flows through the spindle of the machine tool and is supplied to the machining area from the tool mounted at the forward end of the spindle. Japanese Unexamined Patent Publication No. 6-241364 discloses such a through spindle coolant device and a rotary joint for transferring a fluid from a fixed pipe to a rotating pipe of the through spindle coolant device.
However, the rotary joint disclosed in Japanese Unexamined Patent Publication No. 6-241364 does not have an assumption that it would be applied to the cartridge-type spindle device. Therefore, an attempt to use the rotary joint for the cartridge-type spindle has a problem in that the spindle cannot be smoothly pulled off. Specifically, when the rotary joint described in Japanese Unexamined Patent Publication No. 6-241364 is just applied to the cartridge-type spindle device, the rotary joint will be arranged behind the unclamp device of the draw bar. This requires the draw bar to be long or requires support for the bearing in the process, thereby posing a problem that a structure is required in which the draw bar can be separated while being pulled off the spindle.